Biology subjects

Frank, M. W.

Publications and source records attributed to Frank, M. W..

4 recordsLinked to original sources

bioRxiv2026

Enhancement of low-temperature growth of Staphylococcus aureus by low concentrations of antimicrobial unsaturated fatty acids

The incorporation of oleic acid, a physiologically relevant and relatively non-toxic fatty acid, into membrane phospholipids and glycolipids has major impacts on the membrane biophysical properties of Staphylococcus aureus, including the promotion of low-temperature growth. Inclusion of oleic acid in growth media decreased the minimum growth temperature of S. aureus. It has not been studied yet whether other physiologically relevant, yet more antimicrobial straight-chain unsaturated fatty acids (SCUFAs), elicit similar responses. Here, we report that exogenous addition of these antimicrobial SCUFAs at 12{degrees}C led to their incorporation into the membrane lipids in only relatively small amounts, which, however, was sufficient to strongly promote growth at low temperatures. Intriguingly, these SCUFAs showed a preferential incorporation into diglucosyldiacylglyceride (DGDG) over phosphatidyl glycerol, and increased DGDG levels [~] 4-fold in SCUFA-grown S. aureus. Two glycolipid-deficient mutants lost the growth-enhancing effects of SCUFAs at low temperatures and showed increased susceptibility to SCUFAs at 37{degrees}C, suggesting that glycolipids are important membrane components and are required for low-temperature adaptation. The presence of SCUFAs at low temperatures also enhanced the production of the carotenoid staphyloxanthin. Overall, our results suggest that multiple strategies are at play in the membrane lipid remodeling of S. aureus to adapt to the stress of low-temperature growth and likely to other environmental stresses. Incorporation of antimicrobial SCUFAs into membrane lipids may facilitate the insertion of free forms of these SCUFAs into the membrane and be a part of their mode of action.

microbiology↗

bioRxiv2025

Mechanisms of 10-Hydroxyoctadecanoic acid resistance in Streptococcus pneumoniae

Profiles of human nasal colonization consistently demonstrate that Staphylococcus aureus and Streptococcus pneumoniae can co-exist in the nasopharynx. Several studies have demonstrated the antagonist relationship between the two organisms via several molecular mechanisms including competition for nutrients as well as via direct killing by hydrogen peroxide. During nasal colonization, the pneumococcus is in direct contact with the fatty acid h18:0, which is released into the extracellular environment by S. aureus. We report that h18:0 is specifically toxic to the pneumococcus amongst the pathogenic streptococci, providing a unique mechanism for interspecies competition during colonization. Exposure of cells to h18:0 revealed that S. pneumoniae could rapidly adapt to and overcome the observed toxicity. Whole genome analysis revealed the mechanism underlying this resistance being linked to a truncation of a glycosyltransferase in the capsule biosynthesis locus and a genomic inversion in the phase variation locus, leading to altered cell surface charge and membrane lipid composition. These physiological differences in the resistant isolates may aid in repelling toxic, charged fatty acids such as h18:0 from the cell membrane. IMPORTANCEThe pneumococcus and S. aureus are two of the most well-characterized residents of the human nasopharynx; yet much remains unknown regarding how the two bacteria interact. Here, we describe the potential of S. aureus-produced h18:0, whose function and biological impact are still being described, to act as an inter-species competition molecule against S. pneumoniae, and how the pneumococcus can adapt to overcome its toxicity.

microbiology↗

bioRxiv2024

The Bacillus subtilis cell envelope stress-inducible ytpAB operon modulates membrane properties and contributes to bacitracin resistance

Antibiotics that inhibit peptidoglycan synthesis trigger the activation of both specific and general protective responses. {sigma}M responds to diverse antibiotics that inhibit cell wall synthesis. Here, we demonstrate that cell wall inhibiting drugs, such as bacitracin and cefuroxime, induce the {sigma}M-dependent ytpAB operon. YtpA is a predicted hydrolase previously proposed to generate the putative lysophospholipid antibiotic bacilysocin (lysophosphatidylglycerol), and YtpB is the branchpoint enzyme for the synthesis of membrane-localized C35 terpenoids. Using targeted lipidomics we reveal that YtpA is not required for the production of lysophosphatidylglycerol. Nevertheless, ytpA was critical for growth in a mutant strain defective for homeoviscous adaptation due to a lack of genes for the synthesis of branched chain fatty acids and the Des phospholipid desaturase. Consistently, overexpression of ytpA increased membrane fluidity as monitored by fluorescence anisotropy. The ytpA gene contributes to bacitracin resistance in mutants additionally lacking the bceAB or bcrC genes, which directly mediate bacitracin resistance. These epistatic interactions support a model in which {sigma}M-dependent induction of the ytpAB operon helps cells tolerate bacitracin stress, either by facilitating the flipping of the undecaprenyl-phosphate carrier lipid or by impacting the assembly or function of membrane-associated complexes proteins involved in cell wall homeostasis. ImportancePeptidoglycan synthesis inhibitors include some of our most important antibiotics. In Bacillus subtilis, peptidoglycan synthesis inhibitors induce the {sigma}M regulon, which is critical for intrinsic antibiotic resistance. The {sigma}M-dependent ytpAB operon encodes a predicted hydrolase (YtpA) and the enzyme that initiates the synthesis of C35 terpenoids (YtpB). Our results suggest that YtpA is critical in cells defective in homeoviscous adaptation. Further, we find that YtpA functions cooperatively with the BceAB and BcrC proteins in conferring intrinsic resistance to bacitracin, a peptide antibiotic that binds tightly to the UPP lipid carrier that sustains peptidoglycan synthesis.

microbiology↗

bioRxiv2023

Vaginal Lactobacillus fatty acid response mechanisms reveal a novel strategy for bacterial vaginosis treatment

Bacterial vaginosis (BV), a common syndrome characterized by Lactobacillus-deficient vaginal microbiota, is associated with adverse health outcomes. BV often recurs after standard antibiotic therapy in part because antibiotics promote microbiota dominance by Lactobacillus iners instead of Lactobacillus crispatus, which has more beneficial health associations. Strategies to promote L. crispatus and inhibit L. iners are thus needed. We show that oleic acid (OA) and similar long-chain fatty acids simultaneously inhibit L. iners and enhance L. crispatus growth. These phenotypes require OA-inducible genes conserved in L. crispatus and related species, including an oleate hydratase (ohyA) and putative fatty acid efflux pump (farE). FarE mediates OA resistance, while OhyA is robustly active in the human vaginal microbiota and sequesters OA in a derivative form that only ohyA-harboring organisms can exploit. Finally, OA promotes L. crispatus dominance more effectively than antibiotics in an in vitro model of BV, suggesting a novel approach for treatment.

microbiology↗